Rockwell Hardness testing is a system for determining hardness of metallic material. The E 18-03 standard established by ASTM is a detailed description of the Rockwell Hardness testing method.

A 120 degree angle diamond or 1/16” (1.588mm) diameter hard steel ball indenter is pressed into the test piece surface with a preliminary force Po (10kgf) at a depth Do. Then, a main force P1 is added until the total test force, P = Po + P1, is 60kgf for HRA, 100kgf for HRB and 150kgf for HRC, and the indenter increases to a depth D2. Then, the preliminary force Po is unloaded, and the indenter decreases to a depth D1. This results in a depth difference, e = D1 – Do, measured in units of 0.002mm. The hardness reading for HRA and HRC is 100-e, and for HRB is 130-e